1. Field of the Invention
The present invention relates in general to integrated circuits and in particular to polarity independent power supply control methods and systems using the same.
2. Description of the Related Art
Sophisticated design and fabrication techniques are rapidly making practical systems-on-a-chip a reality. In turn, a broad range of personal and commercial hand-held appliances can be constructed which embody a high degree of functionality. These appliances include personal digital assistants, personal digital music players, compact computers, point of sale devices, and Internet access devices, to name only a few of the possibilities.
A number of factors must be addressed when designing a system-on-a-chip. Among other things, the device must be capable of interfacing with a broad range of input/output devices which may be required to support various potential user-defined applications. Moreover, the device must be power efficient while operating at high clock speeds. Additionally, the device should have a large address space to flexibly support a range of possible memory configurations and sizes.
The principles of the present invention are embodied in methods and circuits for controlling power supplies of differing control input polarities. According to one embodiment, a method is disclosed of controlling a power supply having an output activated in response to a first logic level of a control signal and deactivated in response to a second logic level of the control signal. A clock is generated on a second power source and used to time a time -out period of a selected number of clock periods. The state of the output of the power supply is sensed during the time out period. If the state of the output of the power supply is inactive through the timeout period, the first logic level of the control signal is generated to activate the power supply for powering operations of an associated device. At the completion of these operations, the second logic level of the control signal is generated to deactivate the power supply. If the state of the output of the power supply is active during the time-out period, the first logic level of the control signal is maintained while operations of the associated device are powered. At the completion of these operations, the second logic level of the control signal is generated to deactivate the power supply.
Circuits, systems and methods embodying the principles of the present invention have substantial advantages. Among other things, they allow a power supply or similar circuit operating in response to a control signal of arbitrary polarity to be compatible with the associated functional circuitry. Moreover, only a single pin or terminal is required to implement power supply control in the case of an external power supply. Also, no preprogramming or pin strapping is required.